156
LIEUT.-COLONEL SABINE ON TERRESTRIAL MAGNETISM.
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z .
N.w. by N.
-2-12
33 45
31 33
N.W.
—2-07
45 00
42 53
n.w. by w.
—2-42
56 15
53 33
s.w. by w.
-3-52
123 45
119 53
s.w.
— 3-28
135 00
131 32
s.w. by s.
-2-38
146 15
143 37
s.e. by s.
+ 2 45
213 45
216 30
S.E.
+ 3-16
225 00
228 16
s.e. by e.
+ 3-47
236 15
240 02
n.e. by e.
+ 2-08
303 45
305 53
N.E.
+ 2-05
315 00
317 05
n.e. by n.
+ 1-27
326 15
327 42
Employing these values of £*' and ^in the formula
cos £ sin — b cos g sin a tan 6 sin = 0,
and eliminating a tan 6 sin £*', we have
57471 b = 5-6233 ; b = *9785.
Collecting now in one view the values of a, we have as follows:—
1. From the observations at Gillingham near Chatham a = + '0264
2. From the observations at Hobarton. a = + '0272
3. From the observations at Auckland Island . . . a = + '0263
4. From the observations in lat. — 68°30', long. 176°35'a = + -0267
Mean. . . . + -0267
From this near accordance in the values of a, obtained in dips varying from + 69° 05'to — 83° 35', we are warranted in regarding the local attraction in the Erebus as dueto induced magnetism ; and in employing the formulas derived from M. Poisson’sfundamental equations, which are based on the hypothesis of induced magnetismonly, in computing corrections for the observations made on board that ship.
For the value of b we have
From the observations at Gillingham. b = + ‘9874
From the observations at Hobarton. b = + -9865
From the observations at Kerguelen Island . . . b = -\- -9785
Mean . . . + -9841
With these values of a and b, a table of double entry was formed, having for argu-ments £■' and 6; £*' being the compass direction of the ship’s head when an azimuthwas observed, and 6 the inclination taken from the chart formed from the observa-tions of that element on board ship, corrected in the manner that will be shownhereafter ; the corrections for the ship’s local attraction in the general Table of Decli-nations observed in the Erebus have been taken from the Table thus formed.